Junior Cycle · Geometry Lesson 8 of 12

JCHL Geometry 9: Proof of Theorem 6 (Practise)

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Learning work

  • You do NOT need to learn these proofs off for the new Junior Cycle — they are for understanding proofs
  • Theorem 6: the exterior angle of a triangle equals the sum of the two interior opposite angles
  • Use straight angle = 180° and angles-in-a-triangle = 180°, then cancel the shared angle
  • You may use Theorems 1–5 (already proved) inside this proof

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